Substantial heat losses are generated in the operation of an internal combustion engine, and these heat losses must be removed from the engine and dissipated to prevent engine temperatures that can destroy engine lubrication and parts. Water-to-air heat exchangers, commonly called "radiators", are predominantly used to cool internal combustion engines; and water or a water and antifreeze mixture is circulated through the engine as an engine-cooling fluid to absorb, through the inner surfaces of the internal combustion engine, the heat loss generated in the operation of the engine. The heated water is then delivered to the water-to-air heat exchanger or radiator where the heat is transferred from the water to air flowing through an engine radiator. The engine radiator is most frequently located in a position on the vehicle where air can be directed through the heat exchanger as a result of movement of the vehicle driven by the internal combustion engine. Because internal combustion engines are operated while stationary and in vehicles which are not in motion, an engine-driven fan is used to create air flow through the heat exchanger. With the internal combustion engines of vehicles, the radiator is most frequently positioned in front of the engine; and the fan is driven from the crank shaft of the engine. The efficiency of such fans is low, usually in the range of twenty-five percent due to poor blade design and poor air flow around the fan; and such fans drain engine power and reduce the overall efficiency of an engine.
Such water-cooled engines present the further disadvantage of an additional coolant, water, in addition to the oil that is used to lubricate the engine. Water, of course, freezes at 32.degree. F. (0.degree. C.); and the internal combustion engine must be protected against the expansion of freezing water by adding antifreeze into the water. Notwithstanding such protective actions, the use of water, or for that matter, any additional coolant, introduces into the internal combustion engine a further source of unreliable operation. Water introduces a source of corrosion, rust, and cylinder liner cavitation into the engine, and requires additional engine accessories such as pumps, radiators, hoses, belts, and fans.
Fuel consumption and power output are important factors in the operation of an internal combustion engine. The performance of an internal combustion engine can be improved by the introduction of a greater quantity of charge-air, i.e., oxygen available in the combustion chambers of the engine cylinders for combustion. A greater quantity of oxygen in the air-fuel mixture permits more complete combustion, resulting in a greater power output for the engine, better fuel economy, and a reduction in the level of noxious emissions, such as residual hydrocarbons and carbon monoxides present in the exhausted gases.
Volumetric efficiency is a measure of the actual quantity of charge-air in the combustion chamber of an internal combustion engine at the end of the intake stroke relative to the amount of charge-air that could be in the chamber under normal atmospheric conditions. Non-supercharged engines must necessarily have a volumetric efficiency of less than one hundred percent because of the expansion of the charge-air in the combustion chamber due to its heating prior to the closing of the intake valve or valves and the inability to reach atmospheric pressure in the combustion chamber because of air pressure losses due primarily to the restricted intake valve openings. An increase in the volumetric efficiency of an internal combustion engine increases its overall operating efficiency.
One common method of increasing the air quantity available in the engine cylinder combustion chambers is supercharging the combustion chambers through the use of one or more turbochargers. Another method is through the use of a charge-air cooler to cool the charge-air introduced into the chamber, thereby increasing the density of the air and the amount of oxygen to be introduced into the combustion chamber. A further method is using quick opening cams and multiple intake valves in each cylinder to reduce the throttling loss through the intake valves. Such methods increase the volumetric efficiency of an engine.
A turbocharged engine uses an exhaust-driven turbine coupled with a centrifugal compressor to compress ambient air to pressures above atmospheric pressure and to supply the compressed charge-air to the combustion chambers of the cylinders of the engine. This compression process increases the temperature of the air, and it is advantageous to use an aftercooler to cool the charge-air and further increase its density immediately prior to its introduction into the combustion chamber.
Charge-air cooling significantly improves the overall performance of an engine and has been in use for many years. Cooling of the charge-air after its compression by a turbocharger provides a higher charge-air weight to the combustion chamber, allowing the engine to burn more fuel, increasing the power output, improving fuel consumption, decreasing exhaust temperature, decreasing undesirable exhaust emissions, and so on. The lower starting temperature for the combustion process brought about by charge-air cooling can increase the life for the exhaust system, including the turbocharger, and can reduce the mechanical and thermal loads placed on the engine.
Various types of heat exchangers have been used with internal combustion engines to lower the temperature of the charge-air. Coolant-to-air heat exchangers are a type which uses the coolant fluid circulated through the engine block. The engine coolant most often used in a coolant-to-air-type aftercooler is water or a water and antifreeze mixture. In a coolant-to-air-type heat exchanger, however, the temperature of the engine coolant is normally high; and the high temperature of the coolant limits the temperature to which the charge-air can be cooled. Air-to-air heat exchangers are another type which use a flow of ambient air induced through the heat exchanger by vehicle motion or by an engine-driven fan to cool the charge-air. In an air-to-air-type heat exchanger, the lower temperature ambient air is used for cooling; and the temperature of the charge-air can generally be reduced to a level only 35-54.degree. F. (20-30.degree. C.) higher than the initial ambient air temperature.
In a turbocharged engine, the cooling air needed to cool the charge-air may be supplied by extending the inducer blades of the turbocharger compressor and ducting the air from the blade extensions through a separate ductway on the turbocharger to the charge-air aftercooler. Such a system is described in U.S. Pat. No. 3,829,235. A dual outlet compressor produces both the compressed charge-air and the cooling air flow to an air-to-air aftercooler for the charge-air. This system can provide quantities of cooling air for the charge-air to be provided to internal combustion engine cylinders; however, it is not capable of providing large volumes of cooling air required for other heat exchangers that may be used on an internal combustion engine.